Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $236.81   10.816%   $262.4234   $262.42   $262.40   $262.40  
  Purchase #2 $24.76   8.176%   $26.7844   $26.78   $26.80   $26.80  
  Purchase #3 $72.72   8.577%   $78.9572   $78.96   $78.95   $79.00  
  Purchase #4 $41.44   11.697%   $46.2872   $46.29   $46.30   $46.30  
  Purchase #5 $237.49   11.436%   $264.6494   $264.65   $264.65   $264.60  
  Purchase #6 $151.75   6.686%   $161.896   $161.90   $161.90   $161.90  
  Purchase #7 $72.73   13.450%   $82.5122   $82.51   $82.50   $82.50  
  7 purchase totals = $837.70       $923.5098   $923.51   $923.50   $923.50